Previously, we said that when we correct myopia regardless of near vision (see image below), one will use an inadequate corrective power (too strong) while reading if the child reads with his glasses. The visual system is highly adaptable, and additional myopia will be created initially at near, and then will appear at far vision. If we increase simply the correcting glasses, a vicious circle sets and myopia progresses over time … This also applies to some adults whose myopia progresses.
But if we respect the balance that exists between distance and near vision, there will be less effort when focusing and there will be less chance of progression. Unfortunately, this option will not always prevent some children to progress.
When bifocals are necessary, they may incorporate either a small round bifocal that does not show much or we can design a special glass with two zones (far vision at the top and reading at the bottom) and the transition between both areas is invisible. Aesthetic is no longer an obstacle to an adequate correction for children.
Child glasses with a small circular bifocal.
Invisible bifocal suitable for children
I do not really like to use a progressive lens in the case of young myopic children. While glasses with two zones can be adjusted to prevent reading with the upper zone, you never know which area of the progressive lens will be used for reading. If the child leans his head too much, he no longer uses the reading portion essential for the proper control of myopia. The small hallway in the near vision portion of progressives will require the child to move the head and not your eyes. The more we obstruct peripheral vision, to more visual stress we cause.
Progressive lens with narrow reading area
See : http://www.myopiaprevention.org/references_environment.html
Wearing contact lenses
One day or another, many nearsighted young myopic teenagers will want to wear contact lenses for sports or simply to get rid of their glasses…
Regular contact lenses correct only the far vision as glasses that contain only the myopic power, unless they are multifocal. Regular lens wear creates the same situation as to wear glasses for distance vision only: if used for reading, writing and computer for prolonged periods, we may see a more rapid progress of myopia.
So, wearing regular contact lenses should be limited to outdoor and sports wear. As there are many reading and writing activities at school, wearing these contact lenses is not recommended.
Some studies have shown that there is a more rapid myopic progression with contact lenses that correct distance vision only than glasses to see far.
The results found in this study show a definite trend towards poorer accommodative (focusing) and vergence (alignment) function with the use of contact lenses in comparison to glasses. This downward trend is possibly creating a lag in accommodation to reduce associated overconvergence. The higher accommodative lags found in this study with single vision contact lenses indicate that prolonged use of these lenses in near tasks may provoke a continuous hyperopic retinal defocus, a risk factor for the onset and progression of myopia, as indicated in numerous studies.
- Jiménez R, Martínez-Almeida L, Salas C, Ortíz C. Contact lenses vs spectacles in myopes: is there any difference in accommodative and binocular function? Graefes Arch Clin Exp Ophthalmol. 2011 Jun;249(6):925-35.
Before the availability of multifocal contact lenses (which contain both a correction for distance and near vision), a young myope who wanted to wear contact lenses often had to wear reading glasses (spectacles) for near vision in order to counter the effect of the power of his myopic lenses, or remove the contact lenses.
Today, there are multifocal contact lenses specially adapted for young myopes. Here’s an example:
Contact lenses for young myopes: distance vision is at the center of the lens and reading vision lies in the periphery. Example of a contact lens Proclear EP (from Cooper Vision). There are now several other designs.
Bifocal contact lenses are worn during the day and removed at night. They give clear vision for objects far away and objects nearby. Generally they are worn every day although occasionally a day without the lenses will not adversely affect the treatment. The lenses are worn as long as myopia progression is considered a risk.
Bifocal contact lenses have been shown to slow the progression of myopia. The reason they apparently work is not that they reduce the reading effort, which they do, but rather that they create a ring of increased power surrounding central vision that the eye interprets as a “stop signal” for further growth thus reducing the progression.
New studies about bifocal contact lenses in children
There have not been many published studies of soft bifocal contacts being used for myopia control, but the Aller and Wildsoet study showed an 87% reduction in myopia progression for the first year.
Another example of bifocals with alternating zones for distance vision and near vision.Insight® lens (from Cooper Vision)
Dr John Phillips of the University of Auckland, New Zealand described a dual-focus soft lens with a central correction zone and concentric treatment zones. The lens reduced myopic progression by 37 per cent over 20 months in children aged 11-14 years compared with a standard contact lens. Half of those wearing the lens had their myopia progression slowed by 50 per cent or more, but the effect might be up to 80 per cent in future if combined with medication.
- Anstice NS, Phillips JR. Effect of dual-focus soft contact lens wear on axial myopia progression in children. Ophthalmology. 2011 Jun;118(6):1152-61.
Professor Earl Smith of the University of Houston said that myopia control lenses needed to be fitted at an early stage and to very young children.
“In the very near future we’ll be using contact lenses to guide eye growth,” he said. “The principle could be applied to all corrections and might also work for hyperopic eyes. “
- Earl Smith, III OD, PhD (Optometry & Vision Science September 2011 – Volume 88 – Issue 9 – pp 1029-1044
Each of these studies is for one year. Other non-contact lens methods have been found to have less effect after the first year and so it remains to be seen if the contact lens effect is multi-year.
This study has altered our thinking with regard to myopia development and effective treatments to reduce progression. Through extensive research Dr. Smith found that peripheral defocus triggers growth of the eye in a way that leads to an increase of myopia. The signals for this growth are in the peripheral retina. This axial elongation of the eye increases myopia and promotes myopia progression.
For other info or references on bifocal lenses and myopia:
Ortho-K (short for orthokeratology) is a process of gently reshaping the front surface of the eye (in fact, the cornea) to give a clear and comfortable vision. Indeed, the corneal tissue is very malleable and by a slight pressure due to the contact lens, we can change the curvature of the central cornea. This is a non-surgical procedure using specially designed customized contact lenses that are worn only at night and removed when awakening.
The result is a clear vision all day without lens wear during the day and without glasses. The lenses are inserted in the eyes every night since the procedure is not permanent (such as laser treatment), making this therapy safer for children. When the lenses are removed from the eye for a few weeks, the curvature of the cornea slowly returns to its original shape and myopia also returns after several days or weeks, to its initial pre-fitting parameters.
There are many designs of OK lenses but they are mostly equivalent, and all have the goal of reducing myopia overnight by changing the central curvature of the cornea. Orthokeratology is a great way to slow the progression of myopia (see www.myopiaprevention.org).
Children are excellent candidates for orthokeratology because they are motivated, quick to learn how to care for the lenses and respond quickly to the treatment. Ortho-K lenses are also great for kids who participate in sports activities, because they do not have to worry about losing their contact lenses while they are active.
It is a safe alternative to LASIK or other refractive surgery procedures that are not even available for children.
Source : http://www.orthokdoctors.com/what_is_orthokeratology.html
Orthokeratology lens worn on the eye (coloring has been added)